Impact milling apparatus



C. D. FITZ IMPACT MILLING APPARATUS May 18, 1965 2 Sheets-Sheet 1 FiledMarch 24. 1961 IN VEN TOR.

ATTORNEY May 18, 1965 c. D. FITZ IMPACT MILLING APPARATUS Filed March24' 1961 2 Sheets-Sheet 2 INVENTOR. COLEMAN DUDLEY F ITZ ATTORNEY UnitedStates Patent 3,184,172 Ill/{PACT MILLING APPARATUS (Ioleman DudleyFitz, North Caldwell, NJL, assignor to General Mills, inc, a corporationof Delaware Filed Mar. 24, 1961, Ser. No. 98,188 6 Claims. (Cl. 241-194)The present invention relates generally to pulverizing apparatus andmore specifically to improved impact members or hammers for impactmills.

It is known that impact milling requires rapid relative movement betweenan impact member or hammer and air or another gaseous or fluid mediumcontaining particles of the material to be ground. The resulting impactsbetween the particles and the impact member are intended to reduce orpulverize the particles by fragmentation.

In known devices of this type the fluid media, upon sensing the relativeapproach of the usual round pin or fiat-faced impact hammer, movetransversely out around the hammer. The heavier, solid particles werepreviously thought to remain in their original positions or trajectoriesfor impact engagement with the hammer. In reality, however, I haveobserved that the sidewards motion of the fluid medium exerts a lateraldrag upon the particles which tends to deflect the particles from theiroriginal trajectories relative to the hammer. This deflecting force wasfound to be sufiicient to pull some of the smaller particles completelyout of the path of relative movement of the hammer. This action appearsto establish a minimum particle size which is still capable of impingingupon a given hammer. Particles having sizes below this minimum are notstruck and consequently not reduced in size.

The lateral drag of the fluid as it moves around the impact member isalso found to deflect some of the larger particles in a manner whichdecreases the eliectiveness of their impact, even though such particlesdo still strike the impact member. For example, the impact may be at amore acute angle rather than perpendicular to the impact surface, or itmay be at a lower velocity. Thus optimum particle reduction may notoccur.

While devices are known for continually tossing particles back into thepath of the impact surfaces, there eventually exists a static conditionwherein the action of the apparatus no longer overcomes the effect ofthe aerodynamic drag and except for other possible factors, such asfluid turbulence, the particles are no longer capable of furtherreduction by further relative movement against the impact surface of thehammer.

With the above problems and findings in view, it is therefore one objectof the present invention to provide an impact mill having improvedimpact members with surface portions oriented to increase theeffectiveness of the mill.

Another object is an impact mill hammer design which gives the forcesacting upon a particulate material under laminar conditions a greateropportunity of driving the particles against its impact surface.

A further object of the invention is to provide impact hammers for animpact mill, the design of which minimizes the tendency of thesurrounding fluid medium to detect the impact surfaces and moveparticles out of the impact path in advance of particle impingement.

Another object of the invention is to provide improved impact hammersfor an impact mill in which the surfaces of said hammers are designed insuch a manner as to allow a particulate material to impinge thereon atan angle which is most conducive to fracture.

A further object of the invention is to provide an improved impact mill,the capacity of which is increased through the design of impact hammerswhich rapidly reduce a particulate material to its minimum particlesize.

ice

Other objects and advantages will become apparent in the followingspecification and the appended drawings in which:

FIGURE 1 is a front elevational view in partial section of an impactmill illustrating one manner in which improved impact members accordingto the present invention are employed;

FIGURE 2 is a side elevational view taken generally along line 22 ofFIGURE 1;

FIGURE 3 is an enlarged isometric view of a preferred form of impactmember, as embodied in the device of FIGS. 1 and 2;

FIGURES 4 is a diagrammatic view illustrating the fluid flow andparticle impingement with respect to the device of FIGURE 3;

FIGURE 5 is an isometric view of another preferred form of impact hammeraccording to the invention;

FIGURE 6 is a diagrammatic view illustrating fluid flow and particleimpingement with respect to hammer of FIGURE 5;

FIGURE 7 is an isometric view of a modified form of impact memberaccording to another embodiment of the invention; and

FIGURE 8 is a diagrammatic view similar to the diagrammatic view ofFIGURES 4 and 6 showing the resultant air flow and particle impingementwith respect to the device of FIGURE 7.

Before a detailed description of the invention is given, an explanationwill be presented relative to the general construction and operation ofone type of impact mill in which features of the present invention maybe used. It will be understood that the improved impact members orhammers of the instant invention are not limited to employment in theparticular impact mill herein disclosed and that this mill has beenchosen merely as representative of the art in order to illustrate theprincipal features of the invention.

The impact hammer mill it) as shown in FIGURE 1 includes a supportingframe 12 on which are positioned somewhat cylindrically shaped housingmembers or castings 14, i6 and 18 which are secured by bolts 20 to theframe 12. A horizontal shaft or rotor 24 extends centrally throughsuitable openings in the sides of the castings 14, lo and i8 and isjournaled in bearings 22 on the frame 12.

the the The castings thus surround the shaft 24 and form annularchambers 26, 28 and Eli which are concentric with shaft 24. The chamber28 which will be hereinafter referred to as the impact or grindingchamber is located between the castings l4 and 18 within casting 16,while chambers 26 and 36 hereinafter referred to as discharge chambersare positioned on opposite sides of the grinding chamber 28 in castingsl4 and 13 respectively.

The casting 16 is also provided with an integral inlet or opening 32 foradmitting material to the impact chamber 28. Similar openings 34 and 36are provided in the castings l4 and 18 through which material isdischarged as explained later in this specification.

Positioned on the shaft 24 within the impact chamber 28 is a rotor unitwhich includes a pair of separator wheels 38 and 4%) provided with aplurality of radial deflector blades :-2. The deflector blades 4-2 arecircumferentially spaced apart on the side surfaces of the separatorwheels 38 and 45% generally near the periphery thereof and extendradially outward in planes passing through the axis of the shaft 24. Thedeflector blades 42 are secured to the separator wheels by screws 44 andtogether with the separator wheels 38 and 4% form what will later bedescribed as a classifier 56.

Also positioned on the shaft 22 on opposite sides of the separatorwheels 33 and within the discharge chambers 26 and 3d are fans 48 and StThe fans 43 and 51) have integral hub portions 4) and 51 which, when thefans are positioned on the shaft 24, abut against hubs 39 and 41 of theseparator wheels 38 and 40. As noted in the drawings, shaft 24 isprovided generally near the fans 48 and 50 opposite the abutment of saidhubs with threaded surfaces 52 (only one is shown). When the separatorwheels 38 and 4t) and the fans 48 and 56 are positioned on the shaft24,.a pair of lock washers 54 and 56 are placed on the ends of the shaft24 and a pair of lack nuts 57 are secured to the threaded ends of theshaft 14.

to retain the assembly together under compression.

The separator wheels 38 and 49 are provided with an annular opening 58therebetween which extend; around their outer peripheral edge and inwhich are positioned a plurality of impact members or hammers 60. Theimpact members or hammers 60 are equally spaced apart around thecircumference of the separator wheels 38 and 4t and are pivotallymounted between the separator plates by cross pins62 which extend intoopenings 35 and 37 in plates 38 and 40 respectively. The features ofconstruction of these impact members 60 are described in detail later inthis specification.

With reference to the castings 14, 16 and 18, there are circularopenings and 17 along the innerside surfaces of the respective castings14 and 18. These openings are positioned adjacent or concentricallywithin openings 19 and 21 of the casting 16. The openings 15 and 17 aresomewhat smaller than the openings 19 and 21 and the portion of thecasting which surrounds said openings provides annular orifices 66 and68 between the two castings. When the millltl is in operation air isdrawn in through the orifices 66 and 68 from the outside atmosphere bythe fans 48 and 59 and enters the impact chamber 28 being directedinwardly toward the classifier 46 by a plurality of angularly disposedblades 70' spaced circumferentially apart along the side surfaces of thecasting 16.

For operation of the impact mill 10, the rotor 24 is connected to anddriven by a high speed motor (not shown) and asthe shaft 24 revolves, itcarries therewith the separator wheels 38 and 40 and the fans 48 and 50.As the shaft 24 rotates the impact hammers 60 are thrown radiallyoutward and their impact surfaces traverse a circular path within thegrinding chamber 28. Material to be pulverized is admitted through theinlet opening 32 and enters the path of the impact surfaces 61, 63 and65 of the impact hammers 60.

Clearance is provided between the outersurfaces of the hammers 60 andthe inside of the impact chamber 28 which serves as an area for the freecirculation and passage of the material admitted to the chamber. Thecentrifugal force created by the movement of the impact hammers causesthe material to remain substantially in suspension in the air or otherfluid medium in the path of the impact surfaces 61, 63 and 65 and theparticles impinge 'thereon by virtue of the relative movement betweenthe impact members 60 and the air and particles. As their size andgravitational weight become smaller as a result is provided whichincludes a plurality of associated impact surface portions havingdifferent relative angular orientations with respect to the path ofrelative movement between the impactmember and the fluid medium withinthe housing. The angular orientation of at least one of the surfaceportions is adapted to resist lateral deflection The latter particlesare subsequently withdrawn The preferred impact hammers 6%) of theinstant invention, as shown in FIGS. l-4, are provided with a pair ofdeflectors or inclined impact surface portions 61 and 63 which arespaced apart to define an air passage between them. The hammers 60 movein a counterclockwise direction, as viewed in FIG. 2, along a circularpath determined by the rotational movement of the shaft 24, as indicatedby the arrow 64. The preferred impact members 60 also include a thirdimpact surface 65, located rear- Wardly of the inclined surfaces 61 and63, against which some of the particles are channeled at increasedvelocities when the hammer member is moved along its path Within theimpact chamber. It is against these impact surfaces 61, 63 and 65 thatthe particles impinge and are reduced by fragmentation.

FIGURE 3 illustrates further details of the combination of the impacthammer 60 of FIGURES 1 and 2.

I through the opening 69, when the hammer is employed in The impacthammer 69 includes a shank 67 and a plurality of impact bars161, 163 and165 which are provided with the angularly oriented impact surfaceportions 61, 63 and 65. The supporting shank 67 is also provided on itsinner end with a cross pin 62 for attaching the hammer to a suitablemoving or rotating device, as already described with reference to themill 10 of FIGURE 1. The impact bars 161, 163 and 165 having surfaces61, 63 and 65 are located normal to and extend transversely andsymmetrically on each side of the central or radial axis of the shank67. Each is spaced apart from the other to provide in effect, a tortuouspath for the passage of the particle-containing fluid medium. The impactsurfaces or vanes 61 and 63 are radially spaced apart on the shank 67and are inclined inwardly at an angle tending to deflect fluid andparticles toward each other, and thus toward the passage 69 betweenthem. Thus surfaces 61 and 63 provide a substantially concave impactzone adjacent the opening 69 therebetween.

The fluid medium and the particles which thus pass an impact device,then encounter the impact surface 65, which is the front surface ofanother cross bar 165 secured to the shank 67 by set screws 70. Thiscross bar 165 is located in a positioning slot 72 rearward of theopening 69. The impact bars 161 and 163 having surfaces 61 and 63 may beintegral with'the shank as shown or attached thereto by other suitablemeans. Thus particles encountering the hammer member 66 are forced totake a tortuous path around impact surfaces 61, 63 and 65 of the impactmember.

The resultant air flow and subsequent particle impingement against thehammer can be readily understood by viewing FIGURE 4. The fluid mediumindicated generally by the solid lines of numeral 76 passes primarilythrough the. opening 69 and only a small portion is deflected outwardlyaround and out of the path of the impact member. Most of the particles78 thus move inwardly toward the opening 69 and against one or more ofthe impact surface portions 61, 63 and 65. In so doing of the particlesout of the path of the impactmembenand preferably to deflect the fluidand particles into the path of an impact surface portion.

61 and 63 while others near the center of the fluid flow are carriedforward into the path of the impact surface. Since the fluid medium isin effect funneled through the impact zone, the construction providesincreased relative velocity which accelerates the particles towardimpact surface and enables the inertia of the particles to have agreater influence. Thus impingement efiiciency, impactionangle andimpaction velocity are'all substantially maximized to produce rapid andeflicient reduction of particle size. 7 a

In certain applications or situations other embodiments Y are alsouseful such as the one shown in FIGURE 5.

Another embodiment of animpact harrnner according to the invention isindicated generally by the numeral 80 of FIGURE 5. This modification issomewhat like the previous embodiment, but without the rearward impactsurface 55 thereof. The impact hammer 8i accordingly is provided with asimilar supporting shank 82 and a like cross pin 84. The lower end ofthe shank. 82 and the cross pin 84 are identical to the previousembodiment and are therefore interchangeable in the impact mill 1%.

The impact hammer Si) is provided opposite the pin 84 with a first and asecond impact bar or vane 186 and 188 having inclined impact surfaces 86and S8. The impact bars 186 and 183 are radially spaced apart as in theprevious embodiment and their inclined surfaces 85 and 88 face inwardlyto deflect particles and fluid somewhat toward a central opening 90thereoetween, which is created by their spaced relation. The combinedimpact surfaces 86 and 88 thus form a recessed impact surface or zone,which minimizes the tendency of fluid to escape outwardly around theimpact member and drag particles laterally out of the path of thehammer. Here the fluid flow remains chiefly within the path of movementof impact member 80 so that particles will be struck by surfaces 86 and83. Moreover, the increased relative velocity of the fluid passingthrough the narrow opening or slot 90 as in the previous embodimentfurther accelerates the rate of relative movemnt of the particles 92without tending so strongly to drag them out of the path of the hammers.Thus greater impact velocities may be achieved.

FIGURE 6 is a diagrammatic View illustrating this fluid flow andparticle impingement on the hammer 80 of the embodiment of FIGURE 5. Thefluid or air stream is indicated generally by the numeral '76 and isdeflected somewhat inwardly and through the opening 90 at higherrelative velocity. The particles 7 S are therefore projected from thefluid stream at greater impact speeds and a large share of them impingeupon the impact surfaces 86 and 88. Those particles which pass throughthe opening 9%, with or without striking either of surfaces 86 or 88 ofone hammer member, will have further opportunities for impact againstthe similar surfaces of successive hammers.

Another modification of the invention is seen in FIG- URE 7 whereinimproved particle impingement is ob tained by the use of a single hammerhead or member having a concave impact surface. The inner and outerimpact surface portions which are angularly oriented to deflect materialtoward each other are thus parts of a single total impact surface. Thisimpact hammer indicated generally by the numeral 98 includes asupporting shank 1%, an integral hammer head 162, and a support pin E4.The impact hammer head 162 is positioned normal to the shank parallel tothe pin 1% and extends transversely and symmetrically with respect tothe central or radial axis of the shank as shown. The impact hammer head1G2 is substantially elongated, is somewhat narrow in cross section andis provided with a recessed or concave impact surface 1%, that iscoextensive with its transverse length.

The diagrammatic view in FIGURE 8 illustrates the air flow and resultantparticle impingement upon the concave impact surface 166. The air flowis indicated by the numeral 76. While the fluid medium in this case mustnecessarily flow around the impact hammer head 1532 rather than througha passage at its center, the relative angular orientation of the concaveleading edges minimizes the distance at which the fluid starts suchlateral movement ahead of the impact surface. The particles of material,indicated generally by the numeral 78, are thus subjected to lateralaerodynamic drag for as little time as possible.

Moreover, any particles which are drawn outwardly toward the edges ofthe concave impact surface 1% by such drag, tend to impinge upon theimpact surface more nearly perpendicularly to such surface, in View ofthe angular orientation thereof. Also, in view of the minimum timeduring which particles are drawn outwardly by the air stream, many ofthe particles have suflicient momentum to continue toward the center ofthe impact surface 106 and impinge thereon. Thus the concave impactsurface 106 also offers advantages in more efiicient and effectiveimpact reduction.

The impact members or hammers shown and described in the foregoingexamples have a plurality of angularly oriented impact surface portions,at least one of which is oriented to deflect fluid medium and entrainedparticles toward at least one other such surface portion. These hammersor impact members are constructed in such a manner that the forcesacting upon the particles will have the greatest opportunity to drivethem against the hammers. These constructions minimize those adverseeffects of lateral aerodynamic drag which might tend to pull theparticles laterally out of the paths of the impact members. Thus theinertial forces which tend to project the particles in their originalpath or direction against the impact members are used to betteradvantage.

In summary, the features described make it possible to provide suchadvantages as increased impingement efiiciency (i.e. a higher percentageof the particles originally in the path of the impact member willactually be struck by that member), more effective angles of impact, andhigher impact velocities. In the foregoing specification a disclosure ofthe principles of the invention has been presented together with some ofthe embodiments by which the invention can be carried out.

Now, therefore, I claim:

1. In an impact mill having an impact chamber with inlet and outletmeans for admitting and discharging material to be pulverized, and arotor means mounted within said chamber for rotation on a given axis,the improvement comprising impacting means on said rotor means forpulverizing the material admitted to said chamber in response torotation of said rotor means around said axis, said impacting meansincluding a plurality of impact hammers circumferentially spaced aparton said rotor means and movable circumferentially within said impactchamber when said rotor is actuated, each of said impact hammersincluding a radially extending supporting shank, means securing saidshank to said rotor means, first and second radially spaced impactplates extending symmetrically from said shank and parallel to the rotoraxis, said impact plates defining an opening between them and each beingprovided with an inclined impact surface having an angular orientationat the outer edge of its effective impact area adapted to deflectmaterial from that surface toward said opening, and including a thirdimpact plate on said shank, said third plate having an impact surfacelocated rearwardly of the opening between said first and second impactplates for engagement by material passing through said opening.

2. The device of claim 1 wherein each of said impact surfaces issubstantially rectangular in shape and is bounded by acute peripheraledges.

3. In an impact mill having an impact chamber with inlet and outletmeans for admitting and discharging material to be pulverized, and arotor means mounted within said chamber for rotation on a given axis,the improvement comprising impacting means on said rotor means forpulverizing the material admitted to said chamber in response torotation of said rotor means around said axis, said impacting meansincluding a plurality of impact hammers circumferentially spaced aparton said rotor means and movable circumferentially within said impactchamber when said rotor is actuated, each of said impact hammersincluding a radially extending supporting shank, means securing saidshank to said rotor means, first and second radially spaced impactplates extending symmetrically from said shank and parallel to the rotoraxis, said impact plates defining an opening between them and each beingprovided with an inclined total effective impact surface having anangular orientation adapted to deflect material from that surface towardsaid opening.

having an axis perpendicular to said path, first and second impactplates positioned substantially near one end of said supporting shankperpendicular to and symmetrical with said axis of said shank, saidplates being integral with said shank and each provided with anangularly disposed impact surface having an angular orientation withrespect to said path adapted to deflect such fluid medium transverselyof said path toward the other plate. 5. An improved impact hammer for animpact mill including in combination a supporting shank provided withmeans for pivotally attaching said supporting shank to a rotor member ofan impact mill, said shank provided with an impacting member adjacentone end thereof, said impacting member including first, second and thirdsubstantially planar impact surfaces, each of said surfaces being spacedapart from the others and having different angular orientations andlocations such that the planes of said surfaces intersect along a commonline centrally and longitudinally of one of said surfaces.

6. In an impact mill comprising a housing for a fluid medium containingparticles of material to be ground, an impact member within saidhousing, and means for causing rapid relative movement between saidimpact member and said particle containing medium along a predeterminedpath, the improvement in which said impact member comprises a pluralityof impact surfaces spaced with respect to each other transversely andlongitudinally of said path and providing a tortuous passage forrelative movement of the fluid medium through said impact member, atleast two of said impact surfaces being spaced from each othertransversely of said path and defining at least a portion of saidpassage between them for relative movement of said fluid movementtherebe tween, each of said two last mentioned impact surfaces having atotal effective impact area, substantially all of which is angularlyoriented with respect to said path to deflect the fluid mediumtransversely toward said passage.

References Cited by the Examiner UNITED STATES PATENTS r 696,628 4/02Dickson 241 X 845,171 2/07 Gardner 241-194 1,203,314 10/16 Day 2411951,366,512 1/21 Blum 241195 X 1,646,752 10/27 Kimber 241191 X 1,753,4734/30 POISter 241195 X 1,850,244 3/32 Shelton 241-195 2,237,510 4/41Tankersley 241195 2,467,865 4/ 49 Smith 241-194 X 2,700,511 1/55 Denovan241-494 2,822,138 2/58 Olive 241194 7 t FOREIGN PATENTS 175,145 6/53Austria. 958,520 2/57 Germany. 388,337 2/33 Great Britain.

70,780 7/46 Norway.

J. SPENCER OVERHOLSER, Primary Examiner.

ROBERT A. OLEARY, JOHN C. CHRISTIE,

. Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,184,172 May 18, 1965 Coleman Dudley Fitz It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 3, line 8, for "lack" read lock line 45, after "hammers 60."insert As shown, these surfaces 61, 63 and 65 serveas angularly orientedimpactsurface portions of each impact member or hammer 60. line 67,after "is" insert thus line 75, for "an" rea'd-- another column 4, line19, after 3"bars" insert orplates column 5?, line 10, after "surfaces"insert or surface portions line 25, for "movemnt" read movement line 44,after "portions" insert of this concave impact surface, line 45, after"other" insert a comma; column 6, line 6, after "have" insert theirimpact surfaces constructed and arranged to provide same column 6, line74, before "adapted" insert at the outer edge of its effective impactarea Signed and sealed this 14th day of December 1965;

(SEAL) \ttest:

ERNEST W. SWIDER EDWARD J. BRENNER \ttesting Officer Commissioner ofPatents

1. IN AN IMPACT MILL HAVING AN IMPACT CHAMBER WITH INLET AND OUTLETMEANS FOR ADMITTING AND DISCHARGING MATERIAL TO BE PULVERIZED, AND AROTOR MEANS MOUNTED WITHIN SAID CHAMBER FOR ROTATION ON A GIVEN AXIS,THE IMPROVEMENT COMPRISING IMPACTING MEANS ON SAID ROTOR MEANS FORPULVERIZING THE MATERIAL ADMITTED TO SAID CHAMBER IN RESPONSE TOROTATION OF SAID ROTOR MEANS AROUND SAID AXIS, SAID IMPACTING MEANSINCLUDING A PLURALITY OF IMPACT HAMMERS CIRCUMFERENTIALLY SPACED APARTON SAID ROTOR MEANS AND MOVABLE CIRCUMFERENTIALLY WITHIN SAID INPACTCHAMBER WHEN SAID ROTOR IS ACTUATED, EACH OF SAID IMPACT HAMMERSINCLUDING A RADIALLY EXTENDING SUPPORTING SHANK, MEANS SECURING SAIDSHANK TO SAID ROTOR MEANS, FIRST AND SECOND RADIALLY SPACED IMPACTPLATES EXTENDING SYMMETRICALLY FROM SAID SHANK AND PARALLEL TO THE ROTORAXIS, SAID IMPACT PLATES DEFINING AN OPENING BETWEEN THEM AND EACH BEINGPROVIDED WITH AN INCLINED IMPACT SURFACE HAVING AN ANGULAR ORIENTATIONAT THE OUTER EDGE OF ITS EFFECTIVE IMPACT AREA ADAPTED TO DEFLECTMATERIAL FROM THAT SURFACE TOWARD SAID OPENING, AND INCLUDING A THIRDINPACT PLATE ON SAID SHANK, SAID THIRD PLATE HAVING AN IMPACT SURFACELOCATED REARWARDLY OF THE OPENING BETWEEN SAID FIRST AND SECOND INPACTPLATES FOR ENGAGEMENT BY MATERIAL PASSING THROUGH SAID OPENING.